This invention relates to heat exchangers and more particularly to a method for peening a portion of the inside of a small diameter heat exchanger tube to relieve stresses.
Heat exchanger tubes are assembled in heat exchanges and then are held in place by light rolling of the tube in the tubesheet holes. The tubes then have their ends seal welded to the tubesheet and are expanded into engagement with the tubesheet the full depth of the tubesheet. All of these operations are carried out in a manner which minimizes residual tensile stresses. However, such stresses become locked in the tubes when there are severe surface irregularities in the holes, in the tubesheet, or if the tubes are inadvertently deformed in any of the above-mentioned installation procedures. These residual stresses cause premature failure of the tubes unless they are relieved or lowered.